From document JP 2005096493 A, a wheel suspension device with a leaf spring is known. The suspension device comprises a front spring leaf and a rear spring leaf which are connected to each other by bolts. The ends of the front spring leaf and the rear spring leaf are pivotally supported to a side rail. A wheel axis is connected to the front spring leaf. The rear spring leaf has a U-shaped curved part that allows a load-induced deformation of the leaf spring. For the front spring leaf a spring steel or fiber reinforced plastic can be used and, for the rear spring leaf carbon steel or alloyed steel can be used.
From JP 2003335119 A, a leaf spring for a suspension device is known, comprising a thick front spring leaf and a thin rear spring leaf which are connected to each other. The front spring leaf is with its front end pivotally supported at a chassis frame and with its rear end connected to a wheel axle. The rear spring leaf comprises a bent middle part and a rear end that is pivotally supported at the chassis frame. The thinner rear spring leaf is separately produced and heat-treated.
From DE 103 23 693 B3, a sheet metal element made of flexible rolled strip material is known.
From DE 10 2010 015 951 A1, a leaf spring for motor vehicles is known, which is made from fibre reinforced plastic material. The leaf spring is supposed to absorb side load forces and to transfer them to a leaf spring accommodation device. The leaf spring comprises a bending joint portion and a spring portion.
From US 2008/0252033 A1, a leaf spring for a wheel suspension of a motor vehicle is known. The leaf spring is made from a fibre reinforced plastic material and on its ends connected to elastic members, which are mounted on the chassis of the motor vehicle. In an embodiment the ends are bent upwards and are respectively pivotably supported around the longitudinal axis of the motor vehicle in an elastic bushing.
From DE 10 2009 032 919 A1, a spring arrangement with a leaf spring made from fibre compound material is known. The leaf spring has a central portion and two end portions following thereto, which respectively are accommodated in a bearing bracket.
From DE 898 154 A1, a spring suspension system of track vehicles with a leaf spring is known. An end of the leaf spring is formed as an eye by means of which it is supported on the undercarriage. With increasing flexure, the spring ends of the leaf spring are supported on elastic abutments.
From DE 2009 015 662 B3, a spring arrangement with a leaf spring for a motor vehicle is known. The leaf spring is made from a fibre compound material and is held at an end in a clamping member. The clamping member is pivotably mounted on the bearing bracket of the motor vehicle. An abutment is provided on the bearing bracket, against which the clamping member can be supported.
Leaf tensioning springs need to have a very high deformability in the area of the curved portion. This deformability is necessary in order to introduce a tensioning load into the curved portion, besides a bending load, upon increasing deflection. The stiffness of the leaf spring is disproportionately high due to said tensioning load, so that with increasing deflection a strong progression occurs in the spring rate. Because of this high deformability requirements in the curved portion, a glass fibre reinforced plastic material (GRP) is especially suitable as material, which besides a high elasticity and high bearable stresses also has an especially low weight.
It is difficult to satisfy the opposite requirements of a leaf tensioning spring, namely high elasticity in specific areas and high stiffness in other areas.